Innovative smart window covering regulates indoor climate

Recently, research and technical experiments related to energy saving for the air conditioning of residential buildings have been increasing. In this regard, a way forward for smart windows has opened up in England, thanks to the development of a new reconfigurable low-emissivity optical coating that would allow homes to be heated and cooled while significantly reducing thermal energy consumption.

Oxford University researchers, using ultrathin phase change materials, have recently succeeded in creating an adaptable technology to be applied to windows that can "change" according to the seasonal needs of the home.

Testing has been done on an innovative glass with a low-emission coating – which therefore allows for low heat loss, adjustable based on the solar spectrum – that uses a phase change material to control the amount of heat entering the room through the window, without affecting the quality of light.

Thus, two conditions can be created. First, the thermal energy from the sun's infrared rays is absorbed by the glass and re-emitted as heat, which, via transparent electric heaters in the glass substrate, is used to heat the interior of the room. Second, the thermal energy from the sunrays is reflected back outward, to cool the room.

The Oxford research team created a prototype of this technology using an active chalcogenide-based phase change material by which the new glass can adapt to temperature and save energy. The principle is basically as follows: when it is cold in the house, the sun's infrared rays are collected and converted into heat to be fed into the building, thus reducing heating costs. If, on the other hand, it is hot in the house, this smart glass can change state and reflect heat back out, thus reducing the use of air conditioning for cooling.

Therefore, researchers have developed a method to control the optical properties of the coating film and collect (or reflect, depending on season) solar radiation, which would be impossible to achieve by materials with fixed thermal and optical properties.

One of the major aspects of this experiment, as stated by Dr. Youngblood, one of the research authors, is that this smart window is both efficient and aesthetically pleasing: visible light is transmitted almost identically in both states, thanks to the ability to modulate solar heat gain while maintaining a neutral color. This is why no aesthetic change can be noticed in the window when it reflects or collects sunlight.

According to the Oxford University team, the use of windows fitted with this new prototype glass, could generate annual energy savings of between 20-34% (also taking into account the energy required to control the film) compared to the current double-glazed windows that are applied to most typical homes.

According to Harish Bhaskaran, a professor in Oxford's Department of Materials who led the research, significant future studies will be needed before this technology can be marketed, but results show that the concept developed is very promising, and that significant results may be achieved with further study.